This invention relates generally to hybrid vehicles, and more particularly to an energy storage system for applying auxiliary power to a hybrid vehicle, and more particularly to an energy storage system which stores energy by compressing a compressible fluid or gas and converting such stored energy to electrical energy to drive an electric motor/generator which boosts the engine output torque. Under certain operating conditions, the motor/generator generates electrical energy which is used to compress the gas to store energy.
In a hybrid vehicle, a plurality of prime movers are available. Typically such prime movers include an engine, such as an internal combustion engine, and a motor/generator, either interposed between the engine and the vehicle transmission or in parallel thereto for adding torque to supplement the torque provided by the prime mover (i.e. engine or motor). The motor/generator can act as a generator to convert vehicle kinetic energy into electrical energy for storage in a storage device such as a battery. This function as a generator can be in furtherance of the driver""s request for the vehicle to decelerate (regenerative braking) or when the vehicle is operating downhill, or during operation of the engine at high efficiency to generate electrical energy to maintain the charge on the battery.
FIG. 1 schematically shows a hybrid vehicle in accordance with the prior art. The vehicle includes a prime mover, such as an internal combustion engine or electric motor 11, which has a mechanical connection to a motor/generator 13, as for example by a drive shaft 12. The motor/generator may be in parallel or series with the engine and drive the drive shalt through gears or pulleys. The motor/generator drive shaft is coupled to a drive train 14 which drives wheels 16. The drive train has a transmission which may be manual or automatic. Clutches may be interposed in the drive train. A controller or processor 17 receives inputs from the driver, such as accelerator position, brake position, vehicle speed, etc. and controls operation of the prime mover and motor/generator. When the driver begins driving the vehicle, the computer may connect the motor/generator to receive energy from battery 18 and assist in driving the wheels in unison with the prime mover or as the motive power. When the vehicle achieves the desired speed, the engine takes over exclusively. When the driver wishes to accelerate, electrical energy is supplied to the motor/generator to apply auxiliary power to the drive train. This permits the use of a smaller engine and yet achieve desired acceleration. Auxiliary power can also be applied for hill climbing or the like. On the other hand, when the driver applies the brakes, the motor/generator is switched to act as a generator adding load, permitting faster stopping, and generating electricity for the purpose of recharging the battery 18. Likewise, during deceleration or downhill operation it generates electricity which is used to charge the energy storage system. This a brief description of the operation of a hybrid vehicle and its operation and is well-known in the art. Other energy boosters using electric power have included flywheels, capacitors and chemical batteries. Hydro-pneumatic systems have used mechanical means to transfer energy to and from a vehicle.
Operating efficiency improvements to vehicles using hybrid configurations have been mitigated by the availability of a practical means of energy storage. Problems with storing, transferring and effectively controlling the amounts of energy needed for an effective hybrid vehicle configuration have been encountered with chemical batteries, flywheels, capacitors and hydro-pneumatic systems. Problems with each means of energy storage have hampered and delayed the introduction of an effective hybrid. Chemical batteries have been adopted for use with currently available hybrids, but even the most promising batteries have serious problems, and concerns persist. To achieve acceptable regenerative turnaround efficiencies, chemical batteries must be heavy and take up considerable volumetric space. Large size and heavy weight are needed to effectively augment the function of the prime mover in a parallel or series configuration of the motor/generator.
Issues of earnest concern to manufacturers and consumers of hybrid vehicles include the size, weight and initial cost of the battery pack, the limited life span of the battery pack and the high replacement costs. Also of serious concern is the exposure to risk because of explosive gases created during the recharging process and the shear size and toxic nature of the battery materials themselves. Ultimately the costs and problems associated with the disposal and recycling of very large amounts of such toxic materials also make the use of chemical batteries problematic as a means of energy storage.
Hydro-pneumatic storage of energy has proven to be a highly effective and efficient means of storing energy for both series and parallel hybrid configurations. Proven examples of successful hydro-pneumatic systems are well known and their functions are well understood, but serious problems exist with safety. Relatively large diameter high pressure lines must be routed from one point on the vehicle to another. Relatively large volumes of highly pressurized liquid must be transferred from the point of storage to the point of use through these lines. These lines represent an exposure to risk that has been determined to be intolerable. If these problems were eliminated, the feasibility of adopting pressurized gas as an acceptable means of energy storage for a hybrid vehicle would become practical.
It is the object of this invention to provide an energy storage system which utilizes pressurized gas as the means for providing a safe, inexpensive and reliable means of energy storage for use in a hybrid vehicle.
A further object of the invention is to provide a means of energy storage and system which is conveniently and inexpensively adaptable into the drive train of currently produced vehicles with internal combustion engines.
A further object of the invention is to provide a means of energy storage which is conveniently and inexpensively adaptable to the drive train of fuel cell-powered vehicles.
A further object of the invention is to enable a hybrid vehicle to utilize electrical energy for the purpose of pressurizing a gas for the storage of energy, utilizing the stored energy, and, in turn, providing electrical energy back to the hybrid vehicle.
A further object of the invention is to enable electrical current to be controlled by the mechanical manipulation of a pressurized compressible medium.
A further object of the invention is to enable the energy storage means to respond to and interact with the vehicle""s existing electronic engine control system.
A further object of the invention is to enable the energy storage means to respond to and react with the vehicle""s braking system.
A further object of the invention is to allow for a smaller packaging of the power unit by the utilization of an intensifier to convert the high pressures possible in modern lightweight pressure vessels to the lower pressures used by inexpensive and readily available rotating equipment.
A further object of the invention is to enclose the components involving high pressure inside a safety enclosure comprised of materials similar to those used for crash-protection air bags, thus providing an additional supplemental restraint system for the protection of passengers and/or cargo.
This invention relates generally to an energy storage system for use in hybrid vehicles. The system provides auxiliary power to a prime mover of any type including internal combustion engines or fuel cell motors. The energy storage system includes two motor/generators connected in such a fashion that when one acts as a generator, the other acts as a motor, with their roles being reversed periodically. One motor/generator is connected to the prime-mover/drive train and the other motor/generator is connected to a pressure apparatus. The rotation of the motor/generator which is connected to the drive train converts vehicular inertia during deceleration and braking and during periods of highly efficient operation into electrical current. The electrical current is transferred to the second motor/generator where the force of rotation is converted by a hydraulic pump into energy stored in a pressurized gas. A hydraulic motor/pump driven by the energy from the pressurized gas rotates the second motor/generator to provide electrical current to the first motor/generator which is connected to the vehicle drive train. This provides additional motive power for the vehicle during periods of acceleration, hill climbing, maintaining steady speeds over varying terrains and the like.